We are analyzing the neuronal basis of a rapid-onset, long-duration associative learning mechanism in the terrestrial slug, Limax maximus. The learning mechanism is part of the neural control system for feeding. We use behavioral experiments to define the major plastic capabilities of the neural control system for feeding. Neurophysiological and neurochemical experiments aim to define the critical synaptic loci of plastic changes and the causative biophysical and biochemical events which underly them. The proposed behavioral experiments will further characterize the associative learning ability of the isolated cerebral ganglia by testing for long term memory retention times of several days and the higher order conditioning phenomena (second order conditioning, compound conditioning and blocking) shown by the intact animal. Neurophysiological experiments will focus on changes in previously characterized dopaminergic and serotonergic neurons with learning and search for command neurons in the feeding network as potential loci for plastic changes. Neurochemical experiments will extend our observation that dietary choline augments memory retention by testing for the effects of dietary tyrosine and tryptophan on brain levels of dopamine and serotonin and on learning and memory retention. The design of successful therapeutic measures for learning and memory disorders such as senile dementia and Alzheimer's disease would be aided greatly by definition of the basic synaptic changes which underlie normal learning and memory storage. The proposed experiments will contribute to that definition.